Login with Facebook account using php - Facebook Oauth Login.

<?php
/*
 * codrglass.com - Basic configuration and setting
 */

// Facebook API configuration
define('FB_APP_ID', 'Insert_Facebook_App_ID');
define('FB_APP_SECRET', 'Insert_Facebook_App_Secret');
define('FB_REDIRECT_URL', 'Callback_URL');

// Start session
if(!session_id()){
    session_start();
}

// Include the autoloader provided in the SDK
require_once __DIR__ . '/facebook-php-graph-sdk/autoload.php';

// Include required libraries
use Facebook\Facebook;
use Facebook\Exceptions\FacebookResponseException;
use Facebook\Exceptions\FacebookSDKException;

// Call Facebook API
$fb = new Facebook(array(
    'app_id' => FB_APP_ID,
    'app_secret' => FB_APP_SECRET,
    'default_graph_version' => 'v3.2',
));

// Get redirect login helper
$helper = $fb->getRedirectLoginHelper();

// Try to get access token
try {
    if(isset($_SESSION['facebook_access_token'])){
        $accessToken = $_SESSION['facebook_access_token'];
    }else{
          $accessToken = $helper->getAccessToken();
    }
} catch(FacebookResponseException $e) {
     echo 'Graph returned an error: ' . $e->getMessage();
      exit;
} catch(FacebookSDKException $e) {
    echo 'Facebook SDK returned an error: ' . $e->getMessage();
      exit;
}

?>

<?php
// Include configuration file
require_once 'config.php';

if(isset($accessToken)){
    if(isset($_SESSION['facebook_access_token'])){
        $fb->setDefaultAccessToken($_SESSION['facebook_access_token']);
    }else{
        // Put short-lived access token in session
        $_SESSION['facebook_access_token'] = (string) $accessToken;
        
          // OAuth 2.0 client handler helps to manage access tokens
        $oAuth2Client = $fb->getOAuth2Client();
        
        // Exchanges a short-lived access token for a long-lived one
$longAToken=$oAuth2Client->getLongLivedAccessToken($_SESSION['facebook_access_token']);
$longLivedAccessToken =   $longAToken;  
$_SESSION['facebook_access_token'] = (string) $longLivedAccessToken;
        
        // Set default access token to be used in script
        $fb->setDefaultAccessToken($_SESSION['facebook_access_token']);
    }
    
    // Redirect the user back to the same page 
	//if url has "code" parameter in query string
    if(isset($_GET['code'])){
        header('Location: ./');
       $longLivedAccessToken = $longAToken;
    }
    
    // Getting user's profile info from Facebook
try {
 $graphResponse = $fb->get('/me?fields=name,first_name,last_name,email,link,gender,picture');
 $fbUser = $graphResponse->getGraphUser();
    } catch(FacebookResponseException $e) {
        echo 'Graph returned an error: ' . $e->getMessage();
        session_destroy();
        // Redirect user back to app login page
        header("Location: ./");
        exit;
    } catch(FacebookSDKException $e) {
        echo 'Facebook SDK returned an error: ' . $e->getMessage();
        exit;
    }
    
   
    // Getting user's profile data
    $fbUserData = array();
    $fbUserData['oauth_uid']  = !empty($fbUser['id'])?$fbUser['id']:'';
    $fbUserData['first_name'] = !empty($fbUser['first_name'])?$fbUser['first_name']:'';
    $fbUserData['last_name']  = !empty($fbUser['last_name'])?$fbUser['last_name']:'';
    $fbUserData['email']      = !empty($fbUser['email'])?$fbUser['email']:'';
    $fbUserData['picture']    = !empty($fbUser['picture']['url'])?$fbUser['picture']['url']:'';
    $fbUserData['link']       = !empty($fbUser['link'])?$fbUser['link']:'';
   
    $userData = $fbUserData;
    
    // Storing user data in the session
    $_SESSION['userData'] = $userData;
    
    // Get logout url
    $logoutURL = $helper->getLogoutUrl($accessToken, FB_REDIRECT_URL.'logout.php');
    
    // Render Facebook profile data
    if(!empty($userData)){
        
        $_SESSION['userName'] =$userData['first_name'];
        $_SESSION['userPic']='<img src="'.$userData['picture'].'"/>';
        $_SESSION['userId']= '<p><b>Facebook ID:</b> '.$userData['oauth_uid'].'</p>';
        $_SESSION['userFName']= '<p><b>Name:</b> '.$userData['first_name'].'</p>';
        $_SESSION['userEmail']= '<p><b>Email:</b> '.$userData['email'].'</p>';
        $_SESSION['logOUT']= '<p><b>Logout from <a href="'.$logoutURL.'">Facebook</a></p>';
       
        header("Location:home-page.php");
        
    }else{
        $error_out = '<h3 style="color:red">Some problem occurred.</h3>';
    }
}else{
    // Get login url
    $permissions = ['email']; // Optional permissions
    $loginURL = $helper->getLoginUrl(FB_REDIRECT_URL, $permissions);
    
    // Render Facebook login button
    $login-button = '<a href="'.htmlspecialchars($loginURL).'">
	<img src="images/fb-login-btn.png"></a>';
}
?>

<!DOCTYPE html>
<html lang="en-US">
<head>
<title>Login with Facebook using PHP by Coderglass.com</title>
<meta charset="utf-8">
</head>
<body>
<div class="container">
    <div class="fb-box">
        <!-- Display login button -->
        <?php echo $login-button; ?>
    </div>
</div>
</body>
</html>

 <!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>
<center>
<?php 

session_start();

if(isset($_SESSION["userName"])){ 
    
     echo "<h1>You Facebook Details </h1>";
 
      echo  $_SESSION['userPic'];
      echo  $_SESSION['userId'];
      echo  $_SESSION['userFName'];
      echo  $_SESSION['userEmail'];
      echo  $_SESSION['logOUT'];
    
}else{
    
    header("index.php");
}

?>
</center>
</body>
</html>
   

<?php
// Include configuration file
require_once 'config.php';

// Remove access token from session
unset($_SESSION['facebook_access_token']);

unset($_SESSION['userName']);

// Remove user data from session
unset($_SESSION['userData']);

// Redirect to the homepage
header("Location:index.php");
?>